Polarization-adjusted beam operation for materials processing

ABSTRACT

Systems and techniques for optimizing the operation of a beam emitter during material processing maintain an optimal polarization of the beam with respect to the material throughout processing—e.g., even as the beam path varies or the nature or thickness of the material changes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/948,205, filed on Mar. 5, 2014, the entiredisclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

In various embodiments, the present invention relates generally tobeam-emission systems, and more particularly to systems and techniquesfor processing materials.

BACKGROUND

High-power lasers are used in many cutting, etching, annealing, welding,drilling, and soldering applications. As in any materials-processingoperations, efficiency can be a critical limiting factor in terms ofexpense and time; the lower the efficiency, the higher will be the costand/or the slower will be the operation of the laser deployed to processa given material. The brightness and polarization of the laser beam caninfluence efficiency, and different materials (such as copper, aluminum,steel, and so forth) respond differently to beam polarization as theyare processed. Moreover, the thicknesses of these materials can affecttheir polarization response. That is, the nature of a cut or weld mayvary with the beam polarization depending on the material and itsthickness. For example, a linearly polarized processing beam may beabsorbed differently depending on the orientation of the beam'spolarization with respect to the cut front. For this reason,laser-processing systems sometimes utilize circularly or randomlypolarized laser output in order to avoid directionally dependentpolarization responses. While that approach avoids theefficiency-degrading results of unfavorable polarization orientations,it likewise precludes the benefits of favorable orientations.

Accordingly, there is a need for improved systems and techniques forenhancing the efficiency of laser processing operations that exploit thevarying responses to beam polarization that characterize differentmaterials and material thicknesses.

SUMMARY

Embodiments of the invention provide systems and techniques foroptimizing the polarization of a beam during processing, and maintainingthe optimal polarization throughout processing—e.g., even as the beampath varies or the nature or thickness of the material changes.

Accordingly, in a first aspect, the invention relates to a system forprocessing a workpiece. In various embodiments, the system comprise abeam emitter, a positioning device for varying a position of a beam ofthe beam emitter with respect to the workpiece, a variable polarizer forvarying a polarization of the beam, and a controller, coupled to thepositioning device and the polarizer, for operating the beam emittercause the beam to traverse a path across at least a portion of theworkpiece for processing thereof and to maintain a consistentpolarization of the beam with respect to the workpiece along the path.

In various embodiments, the variable polarizer comprises a wave plateand a rotation element, the rotation element being operated by thecontroller. For example, the wave plate may be one or more half-waveplates, one or more quarter-wave plates, or some combination thereof.The beam may, for example, be linearly polarized, with the controlleroperating the rotation element to maintain a polarization directionparallel to the path.

In some embodiments, the system further comprises a memory, accessibleto the controller, for storing data corresponding to the path, and adatabase for storing polarization data for a plurality of materials. Thecontroller is configured to query the database to obtain thepolarization data for a material of the workpiece, and the polarizationdata determines the consistent polarization of the beam. The path mayinclude at least one directional change.

The beam emitter may emit a plurality of beams. The beam emitter may beat least one laser and/or at least one polarized fiber.

In another aspect, the invention pertains to a method of processing aworkpiece. In various embodiments, the method comprises the steps ofoperating a beam emitter to direct a beam traversing a path along theworkpiece to process the workpiece, where the beam has an outputpolarization; and altering the output polarization along at least aportion of the path so as to maintain a consistent polarization of thebeam with respect to the workpiece throughout processing thereof.

The step of processing the workpiece may comprise one or more ofcutting, welding, soldering, drilling, or etching the workpiece. Thestep of altering may comprise directing the beam through a wave plateand varying a rotation angle of the wave plate with respect to the beam.For example, the wave plate may be one or more half-wave plates and/orone or more quarter-wave plates. The beam may, for example, be linearlypolarized, and the altering step maintains a polarization direction ofthe beam parallel to the path.

In some embodiments, the method further comprises the steps of storingdata corresponding to the path, storing polarization data for aplurality of materials, and querying the database to obtain thepolarization data for a material of the workpiece, the polarization datadetermining the consistent polarization of the beam. The path mayinclude at least one directional change.

As used herein, the term “optical element” may refer to any of lenses,mirrors, prisms and the like which redirect, reflect, bend, or in anyother manner optically manipulate electromagnetic radiation. The term“beam” includes any form of directed electromagnetic radiation. “Beamemitters” include any electromagnetic beam-generating device thatgenerates a beam of electromagnetic radiation, and which may or may notbe self-resonating. Beam emitters include free-space (e.g., cavity)laser, fiber lasers, disk lasers, non-solid state lasers and so forth. Abeam emitter may, in some instances, include a back reflective surface,at least one optical-gain medium, and a front reflective surface. Theoptical gain medium refers to increasing the gain of electromagneticradiation and is not limited to the visual, IR or ultraviolet portionsof the electromagnetic spectrum. An emitter may including multiple beamemitters, e.g., a diode bar configured to emit multiple beams. A beammay be single-wavelength or multi-wavelength.

The term “substantially” or “approximately” means ±10% (e.g., by weightor by volume), and in some embodiments, ±5%. The term “consistsessentially of” means excluding other materials that contribute tofunction, unless otherwise defined herein. Nonetheless, such othermaterials may be present, collectively or individually, in traceamounts. Reference throughout this specification to “one example,” “anexample,” “one embodiment.” or “an embodiment” means that a particularfeature, structure, or characteristic described in connection with theexample is included in at least one example of the present technology.Thus, the occurrences of the phrases “in one example,” “in an example,”“one embodiment,” or “an embodiment” in various places throughout thisspecification are not necessarily all referring to the same example.Furthermore, the particular features, structures, routines, steps, orcharacteristics may be combined in any suitable manner in one or moreexamples of the technology. The headings provided herein are forconvenience only and are not intended to limit or interpret the scope ormeaning of the claimed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be more readily understood from the followingdetailed description of the invention, in particular, when taken inconjunction with the drawings, in which:

FIG. 1 illustrates a prior method of cutting a curve out of materialwith the polarization of the cutting beam being fixed.

FIG. 2 illustrates an exemplary adjustment of polarization according tothe cutting path in the material.

FIGS. 3A 3C illustrate an exemplary system for maintaining a consistentbeam polarization relative to a processing direction.

FIG. 4 illustrates a method for cutting or welding a material using anautomatically adjusting polarization beam.

DETAILED DESCRIPTION

Aspects and embodiments relate generally to the field of adjustingpolarization of a lacer beam used in manufacturing, so as to producebetter manufacturing results including less dross and clean cuts andwelds. In various embodiments, therefore, the present invention relatesto optimizing the polarization of a lacer beam with respect to amaterial undergoing processing. More particularly, systems and methodsfor adjusting polarization may involve varying the orientation of a waveplate through which the beam passes in order to selectively vary thepolarization thereof, e.g., based on the geometry, material andthickness of the material undergoing processing and the instantaneousorientation of the beam with respect thereto. The approaches andembodiments described herein may apply to single- and dual-beam outputsystems that use polarization-maintaining optical fibers to deliver theoutput beams from the lacer system to a laser head. In some instances,these laser systems may be wavelength beam-combining systems, whichproduce a multi-wavelength output beam.

Thus, embodiments of the present invention establish an optimalpolarization direction for a given material and maintain this directionwith respect to the processing direction as processing proceeds. This isin contrast to the behavior of prior-art systems, as exemplified in FIG.1, that do not alter the polarization direction. In FIG. 1, a sheet 100of material is processed by a linearly polarized beam that follows adesired cutting path 102, which is curved. The linear polarization,indicated at 104, maintains a fixed orientation regardless of thevarying orientation of the beam relative to the material 100. In manysystems, the optimal beam polarization is parallel to the direction ofprocessing. In FIG. 1, this occurs only once, and in fact, at mostlocations, the polarization is disadvantageously perpendicular to theprocessing direction. This may retard the processing, produce dross,create an imperfect cut, etc.

The optimal behavior for the exemplary system is illustrated FIG. 2: thepolarization orientation 204 of the processing beam remains parallel tothe processing direction throughout the processing path 102. Arepresentative system for accomplishing this is shown in FIGS. 3A 3C.With reference to FIG. 3A, the system 300 includes a laser (or otherbeam emitter, such as a polarized fiber) 305 and a controller 310. Thecontroller 310 controls the operation of the laser 305 (i.e., it activesthe laser 305 and controls beam parameters, such as intensity, asappropriate during processing). The controller also operates aconventional positioning system 315 and a polarizer 320. The positioningsystem may be any controllable optical, mechanical or opto-mechanicalsystem for directing the beam through a processing path along a two- orthree-dimensional workpiece. During processing, the controller mayoperate the positioning system 315 and the laser 305 so that the laserbeam traverses a processing path along the workpiece. The processingpath may be provided by a user and stored in an onboard or remote memory325, which may also store parameters relating to the type of processing(cutting, welding, etc.) and the beam parameters necessary to carry outthat processing. In this regard, a local or remote database 330 maymaintain a library of materials and thicknesses that the system 300 willprocess, and upon user selection of material parameters (type ofmaterial, thickness, etc.), the controller 310 queries the database 330to obtain the corresponding parameter values. The stored values mayinclude a polarization orientation suitable to the material.

As is well understood in the plotting and scanning art, the requisiterelative motion between the beam and the workpiece may be produced byoptical deflection of the beam using a movable mirror, physical movementof the laser using a gantry, lead-screw or other arrangement, and/or amechanical arrangement for moving the workpiece rather than (or inaddition to) the beam. The controller 310 may, in some embodiments,receive feedback regarding the position and/or processing efficacy ofthe beam relative to the workpiece from a feedback unit 335, which willbe connected to suitable monitoring sensors. In response to signals fromthe feedback unit 335, the controller 310 alters the path, compositionand/or polarization of the beam.

In one embodiment shown in FIGS. 31 and 3C, polarization adjustment isaccomplished within a laser head component 350, which is usually thelast opto-mechanical portion of a laser system emitting a beam used inmanufacturing. The laser head 350 includes a collimating lens 355, anadjusting/rotating wave plate 360, and a focusing lens 365 to directbeam 370 onto the surface of the workpiece. The wave plate 360 may be aquarter-wave plate, a half-wave plate, or other wave plate for rotatingthe polarization of the beam 370. With reference to FIGS. 3A-3C, aconventional electro-mechanical rotating device 375 rotates the waveplate 360 under the control of the controller 310 as the beam movesthrough the processing path 102, thus enforcing a consistentpolarization direction of the beam 370 relative to the path 102. Inother configurations, multiple wave plates may be employed andseparately rotated by individual rotating devices 375. The use ofmultiple wave plates may improve response time. The polarization of thebeam 370 is shown at a first orientation 380 a prior to encountering thewave plate 360 and at a second orientation 380 b after passing throughthe wave plate 360.

FIG. 4 illustrates a representative method 400 of operating the system300 to perform a cutting operation. In a first step 410, the userpreprograms the desired path into the system 300 using any suitableinput device or by means of file transfer. In step 420, the controller310 analyzes the curves, features and cutting direction of the path,queries the database 330 as necessary, determines how fast the cut canbe made, and determines the optimal polarization of the laser beamrelative to the cutting direction. In operation, indicated at step 430,the controller 330 operates the laser 305 and subsystems 315, 320 to cutalong the preprogrammed path, maintaining the proper polarizationorientation. If the composition and/or thickness of the material beingprocessed changes, the location and nature of the of change can beprogrammed, and the controller 310 can adjust the laser beam parameters(including polarization) accordingly. It should be noted that theoptimal cutting, welding or manufacturing solution may not necessarilybe the cleanest cut or weld, because additional steps in the process aretypically needed regardless. Thus overall optimization may be based onthe desired output, and the present methods and systems are configuredto produce those desired results whatever they may be. As noted earlier,cutting is only one example of laser processing that may benefit fromthe approach of the present invention.

The controller 310 may be provided as either software, hardware, or somecombination thereof. For example, the system may be implemented on oneor more conventional server-class computers, such as a PC having a CPUboard containing one or more processors such as the Pentium or Celeronfamily of processors manufactured by Intel Corporation of Santa Clara,Calif., the 680×0 and POWER PC family of processors manufactured byMotorola Corporation of Schaumburg, Ill., and/or the ATHLON line ofprocessors manufactured by Advanced Micro Devices, Inc., of Sunnyvale,Calif. The processor may also include a main memory unit for storingprograms and/or data relating to the methods described above. The memorymay include random access memory (RAM), read only memory (ROM), and/orFLASH memory residing on commonly available hardware such as one or moreapplication specific integrated circuits (ASIC), field programmable gatearrays (FPGA), electrically erasable programmable read-only memories(EEPROM), programmable read-only memories (PROM), programmable logicdevices (PLD), or read-only memory devices (ROM). In some embodiments,the programs may be provided using external RAM and/or ROM such asoptical disks, magnetic disks, as well as other commonly used storagedevices. For embodiments in which the functions are provided as one ormore software programs, the programs may be written in any of a numberof high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#.BASIC, various scripting languages, and/or HTML. Additionally, thesoftware may be implemented in an assembly language directed to themicroprocessor resident on a target computer; for example, the softwaremay be implemented in Intel 80×86 assembly language if it is configuredto run on an IBM PC or PC clone. The software may be embodied on anarticle of manufacture including, but not limited to, a floppy disk, ajump drive, a hard disk, an optical disk, a magnetic tape, a PROM, anEPROM, EEPROM, field-programmable gate array, or CD-ROM.

Although the methods described herein for improving processing work wellfor linearly polarized beams (delivered via a free-space laser orpolarization-maintaining fiber), the techniques also work withelliptically polarized beams (dominated by one polarization) as well.For example, a beam from a standard multimode fiber would be likelyelliptically polarized and could benefit from the approach describedherein.

The above description is merely illustrative. Having thus describedseveral aspects of at least one embodiment of this invention includingthe preferred embodiments, it is to be appreciated that variousalterations, modifications, and improvements will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be part of this disclosure, and are intended to bewithin the spirit and scope or the invention. Accordingly, the foregoingdescription and drawings are by way of example only.

What is claimed is: 1.-18. (canceled)
 19. A system for processing aworkpiece along a path extending across at least a portion of a surfaceof the workpiece, a composition and/or a thickness of the workpiecechanging at one or more points along the path, the system comprising: abeam emitter; a positioning device for varying a position, of a beam ofthe beam emitter, at which the beam is emitted onto a surface of theworkpiece; a variable polarizer for varying a polarization of the beam;and a controller, coupled to the positioning device and the polarizer,for (i) operating the beam emitter to cause the beam to traverse thepath for processing of the workpiece, and (ii) maintaining a consistentpolarization of the beam with respect to the workpiece along the path,the controller being configured to alter the polarization of the beam atthe one or more points along the path at which the composition and/orthe thickness of the workpiece changes.
 20. The system of claim 19,wherein the path is curvilinear.
 21. The system of claim 19, wherein thevariable polarizer comprises a wave plate and a rotation element, therotation element being operated by the controller.
 22. The system ofclaim 21, wherein the wave plate is a half-wave plate.
 23. The system ofclaim 21, wherein the wave plate is a quarter-wave plate.
 24. The systemof claim 21, wherein the beam is linearly polarized and the controlleroperates the rotation element to maintain a polarization directionparallel to the path.
 25. The system of claim 19, wherein the beam islinearly polarized and the controller is configured to maintain apolarization direction of the beam parallel to the path.
 26. The systemof claim 19, further comprising: a memory, accessible to the controller,for storing data corresponding to the path; and a database for storingpolarization data for a plurality of materials, wherein the controlleris configured to query the database to obtain the polarization data fora material of the workpiece, the polarization data determining theconsistent polarization of the beam.
 27. The system of claim 19, whereinthe variable polarizer is disposed within a laser head componentconfigured to emit the beam onto the surface of the workpiece, furthercomprising an optical fiber for delivering the beam from the beamemitter to the laser head component.
 28. The system of claim 19, whereinthe beam emitter emits a plurality of beams.
 29. The system of claim 19,wherein the beam emitter emits a multi-wavelength beam.
 30. A method ofprocessing a workpiece using an optical beam, the method comprising:receiving a desired one-dimensional processing path extending across atleast a portion of a surface of the workpiece; computationallydetermining a consistent polarization for the beam along the path basedat least in part on at least one of (i) a composition of the workpiecealong the path, (ii) a thickness of the workpiece along the path, or(iii) a processing direction along the path; operating a beam emitter todirect the beam along the path to process the workpiece, the beam havingan output polarization; and controlling the output polarization of thebeam so as to maintain the consistent polarization of the beam as thebeam traverses the path.
 31. The method of claim 30, wherein the path iscurvilinear.
 32. The method of claim 30, wherein computationallydetermining the consistent polarization for the beam along the pathcomprises querying a database storing beam parameters associated withprocessing types and/or material compositions.
 33. The method of claim30, wherein processing the workpiece comprises at least one of cutting,welding, soldering, drilling, or etching the workpiece.
 34. The methodof claim 30, wherein the controlling step comprises directing the beamthrough a wave plate and varying a rotation angle of the wave plate withrespect to the beam.
 35. The method of claim 34, wherein the wave plateis a half-wave plate.
 36. The method of claim 34, wherein the wave plateis a quarter-wave plate.
 37. The method of claim 30, wherein the beam islinearly polarized and the controlling step maintains a polarizationdirection of the beam parallel to the path.
 38. The method of claim 30,further comprising, while the beam is being directed along the path, (i)receiving feedback from one or more sensors regarding a position and/orprocessing efficacy of the beam relative to the workpiece, and (ii)altering the path and/or the output polarization of the beam in responseto the feedback.